The present invention pertains to a transmission for a motor vehicle, and, more particularly, to a transmission configured to prevent a snap ring, securing a friction element assembly of the transmission, from exiting a groove provided for the snap ring.
In a typical transmission for a motor vehicle, there are a number of friction element assemblies, such as clutches or brakes, each friction element assembly including multiple plates and friction members. During operation of the vehicle, in order to apply a friction element, a piston assembly contacts and then compresses the plates and friction members together. For this compression to occur, movement of the plates and friction members must be restricted in some way. Generally, a snap ring is provided for this purpose, although other portions of the transmission are sometimes used when allowed by the structure of the transmission.
During assembly of the transmission, the friction element assembly is installed followed by the snap ring, which is of the type that is contracted during installation. In order for the snap ring to be installed there must be sufficient room near the friction element assembly for the snap ring to be contracted. After the snap ring is installed, it is allowed to expand back to its default size. When the friction element assembly associated with the snap ring rotates, a centrifugal force acts on the snap ring, which may cause the snap ring to expand if there is room for it to expand. Generally, however, this expansion is arrested by another portion of the transmission, such as a transmission shaft, and the centrifugal force acts to hold the snap ring in place.
In contrast, when the snap ring is of a type that is expanded during installation before being allowed to contract back to its default size, then the centrifugal force caused by rotation of a corresponding friction element assembly will result in the snap ring expanding and this expansion will not be sufficiently arrested. This is because space must be provided for the snap ring to be expanded during installation and this space also allows the snap ring to expand during rotation of the friction element. As a result, this type of snap ring is not typically used for such applications since the expanded snap ring can exit its installation position during operation. If that occurs, the friction element assembly corresponding to that snap ring cannot be actuated by its piston assembly. However as transmission designs become increasingly complex, it is not always possible to arrange friction element assemblies such, that the use of such snap rings is avoided. Therefore, there is a need in the art for a transmission design that allows for the installation of a snap ring that is expanded during installation, and that prevents the snap ring from moving once installed.